5 - Heat Capacity, Phase Change, and Colligative Properties

Question 1

*Pure substances only have ?

*but a system may _____ of solid and liquid phases, but only one gas phase.

Heat Capacity=

C =     

*If while being heated, no PV work is done by a system at rest, nearly all the heat energy goes into increasing the ______

*If the system is allowed to expand at constant pressure, some energy leaves the system as work and the temperature increase_________

*Constant pressure heat capacities are greater than __________

Answer 1

*Pure substances only have one gas and one solid phase.

*but a system may have a number of solid and liquid phases, but only one gas phase.

Heat Capacity= is a measure of the energy change needed to change the temperature of a substance.
OR the heat capacity of a substance as the amount of energy a substance can absorb per unit of temperature change.

C =     _  q_
         (delta) t

*If while being heated, no PV work is done by a system at rest, nearly all the heat energy goes into increasing the temperature.

*If the system is allowed to expand at constant pressure, some energy leaves the system as work and the temperature increase is diminished.

*Constant pressure heat capacities are greater than constant volume heat capacities*

Question 2

Q =

Specific heat capacity= q =

C water=

Coffee cup calorimeter=

Bomb calorimeter=

Answer 2

Q = C(delta)T

Specific heat capacity= q = mc(delta)T

C water= 1 cal g^-1 (degree)C^-1

Coffee cup calorimeter= is an example of a constant pressure calorimeter because it measures energy change at atmospheric pressure. It is used to measure heats of reaction.

Bomb calorimeter= measures energy change at constant volume. A bomb calorimeter tells us the internal energy change in a reaction.

Question 3

Points where heat capacity is infinite=

Heat of fusion=

Heat of vaporization=

*_____ occurs when the partial pressure above a liquid is less than the liquid’s vapor pressure, but the atmospheric pressure is greater than the vapor pressure. Under these conditions, the liquid evaporates rather than _____

Answer 3

Points where heat capacity is infinite= normal melting point and normal boiling point.

Heat of fusion= the enthalpy change associated with melting

Heat of vaporization= the enthalpy change associated with boiling

*evaporation occurs when the partial pressure above a liquid is less than the liquid’s vapor pressure, but the atmospheric pressure is greater than the vapor pressure. Under these conditions, the liquid evaporates rather than boil.

Question 4

Phase diagram=

Triple point=

Critical temperature=

Critical pressure=

Critical point=

Answer 4

Phase diagram= indicates the phase of a substance at different pressures and temperatures.

Triple point= one point where the substance can exist in equilibrium as a solid, liquid, or gas.

Critical temperature= a temperature where the substance cannot be liquefied no matter what pressure is applied.

Critical pressure= pressure required to produce liquefaction while the substance is at the critical temperature.

Critical point= together critical point and critical temperature equal this.

Question 5

Colligative=

Boiling point elevation= (delta)T =

Freezing point elevation= (delta)T =

Answer 5

Colligative= properties that depend upon number, not kind. For ex: vapor pressure, boiling point, freezing point, and osmotic pressure.

Boiling point elevation= (delta)T = K(b)mi

Freezing point elevation= (delta)T = K(f)mi

Question 6

*Substance boils when its vapor pressure equals the _________

*using nonvolatile solute equations, be sure to consider the number of _________

*For BP and freezing point calculations ________ is used instead of molarity because molality doesn’t change _______________

Answer 6

*Substance boils when its vapor pressure equals the local atmospheric pressure.

*using nonvolatile solute equations, be sure to consider the number of particles after dissociation.

*For BP and freezing point calculations molality is used instead of molarity because molality doesn’t change with temperature while molarity does.

Question 7

Osmotic pressure=
Osmotic pressure= (equation)

*BP is elevated when addition of a _______ is added, and Freezing point depressed with addition of ________ is added.

Answer 7

Osmotic pressure= is a measure of the tendency of water to move into a solution via osmosis.
Osmotic pressure= iMRT

*BP is elevated when addition of a nonvolatile solute is added, and Freezing point depressed with addition of nonvolatile solute is added.